1. Field of the Invention
This invention relates to improvements in and relating to the heat sink for electronic apparatus, which is provided with such heat source as transistors and thyristors and in which heat is dissipated into atmosphere by thermal conduction.
2. Description of the Prior Art
Up to date, the capacity of transistors, thyristors and other electronic apparatus parts are on an increasing trend with accompanied increase of thermal loss, while the size of the electronic apparatus themselves is reducing. This means a tendency of increase of the temperature inside the apparatus. In this respect, for maintaining the performance of the apparatus and extending the life thereof it is necessary to dissipate the internal heat into the outside and keep low inside temperature. Usually, the end is achieved with a heat sink, on which electronic apparatus parts are mounted so that heat is radiated through it.
Hitherto, there are two kinds of heat sink of this type. FIG. 1 shows a heat sink 8 of one of these kinds. The heat sink 8, which is extrusion molded mostly from a light metal such as aluminum, has a comb-shaped sectional profile and is cut to a desired length, and a heat source 6 such as a power transistor is mounted by suitable means 10 such as screws on the bottom of the heat sink 8. This kind of heat sink may also use other metals than light metals, and also it may be formed by casting or machine processing as well as extrusion molding.
With this heat sink the heat radiation area is small, while the other kind of heat sink, which is shown in FIG. 2, has large capacity. This heat sink 9 is formed by alternately stacking corrugated fins 2 and separator sheets 3, applying side bars 4 to one side of the stack and a bottom plate 7 to the other side and brazing together all the parts, and heat source 6 such as a power transistor is mounted by suitable means 10 such as screws on the bottom plate 7.
With this type of heat sink shown in FIG. 2, however, although the brazing of the corrugated fins 2 to the separator sheets 3, bottom plate 7 and side bars 4 and brazing of the separator sheets 3 and side bars 4 are substantially perfectly made, the brazing of the bottom plate 7 and separator sheets 4 is difficult because the contact area involved is small, giving rise to high thermal resistance in these portions and tending to reduce the heat radiation performance. The contact area between each corrugated fin 2 and each separator 3 is also small, but the brazing in these portions has no bearing upon the mechanical strength of the heat sink as a whole, and also they are soldered together at many points, so there is no problem.
In another aspect, since the size of the heat sink is determined by the size of the bottom plate, different bottom plates of various sizes have to be prepared in case when heat sinks of various sizes are to be produced, and this has been a drawback from the standpoint of improving the productivity.